@Hernant: That message tells you all you need to know about editing in place: vi is trying to copy it over to /tmp to work on. I think vim will do the same thing, and it does like to create a backup in the same directory.
–
David ThornleyAug 27 '10 at 21:50

5 Answers
5

Try using hexedit I haven't tried it on HP-UX but it should work. It allows you to move to a location in a file and truncate. I'm pretty sure that it does not read the whole file in but just seeks to the appropriate location for display.

Usage is fairly simple once you have launched it the arrow keys allow you to move around. F1 gives help. Ctrl-G moves to a location in the file (hint: to move to end use the size of the file from the bottom row of the display). Position the cursor on the first byte that you want to truncate and then press Escape T once you confirm the truncate will have been done. Ctrl-x exits.

Use a tool that gives you access to the truncate system call. You can do it with only POSIX tools. Warning, typed into a browser; be especially careful as dd is even more unforgiving of errors than the usual unix command. 123456 is the number of bytes to keep.